Soluble alkali metal salt removal from substantially non-polar liquids

ABSTRACT

A process for removing soluble alkali metals from substantially non-polar organic liquid esters is described. The process comprises adding a hydroxy-substituted lower aliphatic saturated dicarboxylic acid to substantially non-polar liquid esters containing alkali metals in salt form, particularly lithium salts, in solution. The hydroxy-substituted saturated dicarboxylic acids form solid insoluble crystalline alkali metal salts in such liquids permitting the separation of the alkali metal moieties from the medium by conventional methods. The presence of dissolved alkali metal salts is undesirable in that it interferes with the end use of such liquid esters.

United States Patent Puhk [151 3,678,097 1 July 18,1972

SOLUBLE ALKALI METAL SALT REMOVAL FROM SUBSTANTIALLY NON-POLAR LIQUIDSContinuation-impart of Ser. No. 709,214, Feb. 29, 1968, abandoned.

Inventor:

US. Cl. ..260/486 R, 260/410.6, 260/4l0.7,

260/406 B Int. Cl. C07c 69/54 Field of Search ..260/486 R, 486 BReferences Cited UNITED STATES PATENTS 3/1965 Cour ..260/486 3,314,9884/1967 Nemecetal ..260/486 Primary Examiner-Lorraine A. WeinbergerAssistant Examiner-Paul J. Killos Attomey-Harold M. Baum, Merton H.Douthitt, Howard G. Bruss, Russell L. Brewer and James E. Carson [57]ABSTRACT A process for removing soluble alkali metals from substantiallynon-polar organic liquid esters is described. The process comprisesadding a hydroxy-substituted lower aliphatic saturated dicarboxylic acidto substantially non-polar liquid esters containing alkali metals insalt form, particularly lithium salts, in solution. Thehydroxy-substituted saturated dicarboxylic acids form solid insolublecrystalline alkali metal salts in such liquids permitting the separationof the alkali metal moieties from the medium by conventional methods.The presence of dissolved alkali metal salts is undesirable in that itinterferes with the end use of such liquid esters.

6 Claims, No Drawings SOLUBLE ALKALI METAL SALT REMOVAL FROMSUBSTANTIALLY NON-POLAR LIQUIDS This application is aContinuation-in-Part of pending U.S. patent application, Ser. No.709,214, tiled in the US. Pat. Office Feb. 29, 1968, now abandoned, inthe name of l-leino Puhk and assigned to the assignee as the instantapplication.

The closestprior art known to applicant is in the file of theabove-mentioned patent application.

The invention relates to the removal of alkali metals, particularlylithium, from non-polar organic liquid esters and more particularly to aprocess in which such esters having alkali metal salts dissolved thereinare precipitated by the addition of a hydroxy-substituted loweraliphatic saturated dicarboxylic acid.

The invention is advantageous in that it facilitates the almostquantitative removal of alkali metals, particularly lithium, fromorganic esters, particularly hydroxy-substituted esters of ethylenicallyunsaturated monocarboxylic acids. The presence of soluble alkali metalsalts in such esters in undesirablesince such salts often interfere withthe end use of the liquids.

The present invention provides a process for removing soluble alkalimetals from the above-described esters which comprises the steps of a.adding to a medium consisting essentially of a hydroxy alkyl ester of anethylenically unsaturated monocarboxylic acid which contains minuteamounts of lithium salts dissolved therein a hydroxy-substituted loweraliphatic saturated dicarboxylic acid in an amount sufficient to form asolid lithium salt of said dicarboxylic acid in said medium and b.separating said salt from said medium.

Alkali metals in the form of salts occur widely in solution in smallamounts in substantially non-polar organic liquid esters due to themethods by which such liquids are obtained. By way of example, whenliquid organic esters are formed by reacting an alcohol or an alkyleneoxide with a carboxylic acid, an alkali metal salt is employed tocatalyze the esterification reaction. The presence of alkali metalresidues in the finished ester is disadvantageous in that certain estersdecompose or are otherwise altered by time due to the presence of suchalkali metals.

The present invention is based on the discovery that when ahydroxy-substituted saturated lower aliphatic dicarboxylic acid is addedto a liquid medium having one or more alkali metal salts dissolvedtherein, the hydroxy-substituted dicarboxylic acid preferentially reactswith the soluble alkali metal salt to form an insoluble alkali metalsalt by virtue of its reaction. The resulting precipitated solids can bereadily removed by conventional methods such as filtration, decantation,centrifugation, and the like.

Alkali metal salts such as sodium, potassium, and lithium are usuallyonly slightly soluble in such organic liquid esters but are oftenpresent in amounts up to 1,000 parts per million Li. and in suchconcentrations usually interfere with the stability of the liquidorganic ester or with its end use. The addi tion of thehydroxy-substituted dicarboxylic acid usually reduces the concentrationof such alkali metal salts to as low as l parts per million or less inthe liquid organic ester medium.

A wide variety of hydroxy-substituted lower aliphatic saturateddicarboxylic acids can be employed in the processes of this invention.Examples of a hydroxy-substituted saturated lower aliphatic dicarboxylicacids include monohydroxy dicarboxylic acids such as tartronic(hydroxymalonic), malic (hydroxy succinic acids); dihydroxy dicarboxylicacids such as tartaric (dihydroxy succinic acid; polyhydroxydicarboxylic acids, including trihydroxy glutaric and saccharic(tetrahydroxy adipic acid and the like). Of these, monohydroxydicarboxylic acids are preferred for economic reasons and because it hasbeen found to form crystalline precipitates which can be readilyfiltered to remove alkali metals almost quantitatively from liquidorganic esters as herein described.

One advantageous embodiment of a process of this invention comprises theremoval of alkali metals from esters in which alkaline metal salts havebeen used to catalyze the'reaction between an acid and a lower alkyleneoxide. Where such esters comprise the reaction product of ana,fi-ethylenically unsaturated carboxylic acid and a lower alkyleneoxide, the presence of the alkali metal tends to promote the formationof undesirable byproducts including products such as homopolymers of theester monomer. Also, the presence of alkali metals in the liquid organicesters often interferes with the properties of products such aspolyester polymers which are prepared by using the ester as onemonomeric component of the polymer system.

By way of example, alkali metal salts such as sodium, potassium,and-.lithium, chlorides, carbonates, acrylates, methacrylates, and thelike are often used as catalysts in the reaction between anethylenically unsaturated monocarboxylic acid and a lower alkyleneoxide, and an alkali metal salt is always present in the resultantliquid ester. In one embodiment of a process falling within the scope ofthe invention the removal of an alkali metal salt is accomplished byadding one of the hereinbefore described hydroxy-substituted saturatedaliphatic dicarboxylic acids to the liquid organic ester immediatelyafter its preparation.

The preparation of liquid organic esters with which the presentinvention is concerned is usually accomplished by reacting a polyol or alower alkylene glycol with an 01,13- ethylenically unsaturatedmonocarboxylic acid. Examples of such unsaturated monocarboxylic acidsinclude acrylic, methacrylic, crotonic, isocrotonic, vinylacetic,tiglic, angelic, senecioic, teracrylic, hypogeic, oleic, elaidic,erucic, brassidic, behenic, etc., acids.

Examples of polyhydroxy alcohols and lower alkylene oxides which may bereacted with the aforementioned monocarboxylic acids include, forexample, glycerine, ethylene glycol, propylene glycol, butylene glycol,etc., and ethylene, propylene, and butylene oxides.

When reacted with a,B-ethylenically unsaturated monocarboxylic acidsthese materials form hydroxy-substituted alkyl esters of such acids and,the reaction is usually catalyzed by an organic amine or an alkali metalsalt. The lower alkylene oxide, when employed, can be reacted with anyof the above acids and the reaction is usually carried out in thepresence of a conventional inhibitor such as quinone antioxident or ahydroquinone or derivative thereof, preferably hydroquinone monomethylether (sometimes referred to as MEHQ) and a catalyst which isusually a potassium or a lithium salt. The reaction is often, althoughnot necessarily, conducted in a hydrocarbon solvent such as xylene ortoluene. The resultant product is an ester of a mixture of ester withthe solvent containing the ester and small amounts of the inhibitor andalkali metal salt hereinbefore described.

The addition of one of the aforementioned hydroxy-substituted saturatedlower aliphatic dicarboxylic acids to the liquid ester precipitates thealkali metal by virtue of the formation of a solid crystallinecarboxylic acid salt of the alkali metal. Surprisingly, when anunsubstituted saturated dicarboxylic acid such as, for example, oxalicacid, is added to such liquid esters, an amorphous dispersion is formedwhich can be filtered only with great difficulty.

The amount of hydroxy-substituted dicarboxylic acid which is added tothe liquid organic ester medium can vary considerably but will depend toa large extent upon the amount of soluble alkali metalsalt in theliquid. Usually a stoichiometric amount of hydroxy-substituteddicarboxylic acid is added in order to quantatively remove the alkalimetal without leaving a significant amount of free unreactedhydroxy-substituted dicarboxylic acid in the medium. The amount ofalkali metal initially present in the medium can be readily determinedby conventional analytical methods, or can be computed by determiningthe amount of alkali metal salt which precipitated from the liquidorganic ester medium as the reaction between the a,fi-ethylenicallyunsaturated monocarboxylic acid and the lower alkylene oxide approachcompletion.

In the foregoing embodiments of the process of this invention, less thanparts per million of alkali metal usually remain in the liquid organicester medium after the addition of the hydroxy-substituted saturatedlower aliphatic dicarboxylic acid and the separation of the salt alkalimetal salt therefrom. 1f alkali metal salts, particularly lithium salts,are present in the medium in amounts above about 10-25 parts per millionparts of ester are not removed by the addition of hydroxy-substitutedsaturated lower dicarboxylic acid, the liquid esters will sometimes tendto form diesters and in some instances homopolymers. Furthermore, as theliquid esters containing alkali metal salts in such higher amounts areused as one monomeric component of a mixture of monomers in thesynthesis of polyester polymers and the polyester polymers are cured toproduce films, the resultant cured films will not have the moistureorthe weather-resistance desired or expected because thealkali-metal-containing films, when exposed to water, will be attackeddue to the leechability of the alkali metal salt residually incorporatedin the film. Removal of alkali metal salts from the organic estersstabilizes the monomeric esters and prevents the attack by water ofcured films containing them.

It is to be understood that a hydroxy-substituted saturated loweraliphatic monocarboxylic acid can be added to almost any liquid organicester medium containing an alkali metal to effect the removal of thealkali metal therefrom. Thus, as will be evident hereinafter from thespecific examples, alkali metal salts can be removed from such esters atany time wherein they present problems such as, for example, of high ashcontent, etc.

It is unexpected that a hydroxy-substituted, saturated lower aliphaticdicarboxylic acid would react with an alkali metal or an alkali metalsalt to form an insoluble crystalline precipitate and to effect theremoval of alkali metal such as lithium from substantially non-polarorganic esters in view of the fact that saturated unsubstituteddicarboxylic acids and hydroxy-substituted monocarboxylic acids do notform crystalline precipitates with alkali metals in substantiallynon-polar liquid organic esters but form amorphous precipitates whichare difficult or virtually impossible to remove by filtration.

The following specific examples are intended to illustrate the inventionbut not to limit the scope thereof, parts and percentages being byweight unless otherwise specified.

EXAMPLE 1 To a reactor equipped with gas introduction and venting means,a thermometer, heating coils, and mechanical agitator, there was added597 pounds of glacial methacrylic acid. Thereafter there was added toand dissolved in the methacrylic acid 176 grams of hydroquinonemethylether(ME1-1Q). The total hydroquinone inhibitor present in themethacrylic acid was 900 parts per million parts of the methacrylicacid. A nitrogen blanket was introduced into the reactor and slowagitation of the methacrylic acid solution was begun. Thereafter, whileagitation was continued, 8,108 grams of lithium carbonate was added andthe reactor was vented for one-half hour to pennit the escape of carbondioxide which evolved from the lithium carbonate-glacial methacrylicacid mixture.

After the evolution of the acrbon dioxide was complete, the reactor wassealed and the contents thereof heated to 185 F. with continuingagitation. The contents of the reactor consisted of a mixture ofmethacrylic acid, lithium methacrylate, and MEI-1Q. Thereafter,propylene oxide was added over a period of two to six hours until atotal of 437 pounds of propylene oxide had been added. During theaddition of propylene oxide and a subsequent hold, a period of from sixto ten hours, the acid number fell and the reaction mixture was helduntil a minimum acid number was obtained. The pressure in the reactorwas maintained at between 30 and 60 psig and the temperature of thecontents of the reactor was maintained at 185 F. During the addition ofthe propylene oxide and the subsequent holding period, the acid numberof the contents of the reactor, which was initially 376, fell to 12.5.Thereafter, the reactor contents were cooled to F., the reactor wasvented and a precipitate consisting essentially of liquid methacrylatewas removed by filtration. The amount of propylene oxide added was suchthat a minor molar excess of propylene oxide was present in the reactorduring the removal of the lithium methacrylate. The crude filtrate wasthen charged back into the reactor and heated to F. The filteredmaterial, which consisted essentially of hydroxy propyl methacrylate,contained 1,050 parts per million of lithium as lithium methacrylate. Tothis organic liquid ester there was added 16.3 pounds of malic acid. Themixture was agitated for one and one-half hours at 150 F after whichvacuum was applied to remove excess propylene oxide. The productobtained consisted essentially of hydroxy propyl methacrylate havingsuspended therein crystals of lithium malate. The crystals were removedby filtration and the final product consisted of 830 pounds of hydroxypropyl methacrylate which had an acid number of 25. The lithium contentof the product determined by microanalytical techniques was less than 10parts per million, expressed as metallic lithium.

EXAMPLE 2 The process of Example 1 was repeated except that 331 poundsof ethylene oxide were used in place of the propylene oxide employed inthat example. Upon the removal of lithium malate, water-white liquidhydroxyethyl methacrylate was obtained.

in the foregoing examples, when the malic acid addition step wasomitted, the products contained in excess of 1,000 parts of lithium aslithium methacrylate per million parts of ester and were unsuitable foruse in the preparation of thermosetting acrylic resins due to poorviscosity control of the resins and to the poor quality of resultantcure films which were tested for water resistance.

EXAMPLE 3 The process of Example 1 was repeated except that tartronicacid was employed in place of the malic acid employed in that example.Substantially the same lithium-free product was obtained.

EXAMPLE 4 The process of Example 1 was repeated except that tartaricacid was employed in place of the malic acid employed in that example.Crystalline lithium tartrate was precipitated and upon removal from thehydroxy propyl methacrylate, a waterwhite monomeric liquid substantiallyfree of lithium was obtained.

EXAMPLE 5 The procedure of Example 1 was repeated except that acrylicacid was employed in place of the methacrylic acid employed in thatexample. Upon addition of the malic acid, crystalline lithium malateprecipitated from the hydroxy propyl acrylate and was removed byfiltration to produce a clear product consisting essentially ofmonomeric hydroxy propyl acrylate.

EXAMPLE 6 The process of Example 1 was repeated except that ethyleneoxide and crotonic acid replaced the propylene oxide and methacrylicacid employed in that example. The resultant product consistedsubstantially of hydroxy ethyl crotonate which contained prior to theaddition of malic acid 1,000 parts per million of lithium. After theaddition of lithium malate, the product, which was a water-white liquid,contained less than 10 parts per million oflithium.

EXAMPLE 7 The process of Example 1 was repeated except that crotonicacid was employed in place of the methacrylic acid employed in thatexample. The resultant product consisted substantially of hydroxy propylcrotonate which contained, prior to the addition of malic acid, 1 10parts per million of lithium as lithium crotonate. After the addition ofthe malic acid and subsequent filtration thereof, the product, which wasa water-white liquid, contained no more than 60 parts per million oflithium.

in the foregoing examples, when propionic or butyric acid are added tothe ester mixtures, no precipitate occurs. On the other hand, when adicarboxylic acid, such as oxalic or glutaric acid, is added to theliquid esters, filtration becomes very difficult and/or virtuallyimpossible.

What is claimed is:

l. A process for removing lithium from a liquid medium consistingessentially of a hydroxy alkyl ester of an a, B- ethylenicallyunsaturated monocarboxylic acid which contains a small amount of lithiumcomprises the steps of:

a. adding to said medium a hydroxy-substituted lower aliphatic saturateddicarboxylic acid in an amount sufficient to form a solid lithium saltof said dicarboxylic acid in said medium and b. separating said saltfrom said medium.

2. The process of claim 1 wherein the hydroxy-substituted loweraliphatic saturated dicarboxylic acid is malic acid.

3. The process of claim 1 wherein the liquid medium is selected from thegroup consisting of hydroxy alkyl esters of acrylic and methacrylicacid.

4. The process of claim 1 wherein the liquid is selected from the groupconsisting of hydroxy ethyl and hydroxy propyl esters.

5. The process of claim I wherein the liquid is hydroxy propylmethacrylate.

6. The process of claim 5 wherein the hydroxy alkyl ester is hydroxypropyl acrylate.

2. The process of claim 1 wherein the hydroxy-substituted loweraliphatic saturated dicarboxylic acid is malic acid.
 3. The process ofclaim 1 wherein the liquid medium is selected from the group consistingof hydroxy alkyl esters of acrylic and methacrylic acid.
 4. The processof claim 1 wherein the liquid is selected from the group consisting ofhydroxy ethyl and hydroxy propyl esters.
 5. The process of claim 1wherein the liquid is hydroxy propyl methacrylate.
 6. The process ofclaim 5 wherein the hydroxy alkyl ester is hydroxy propyl acrylate.